Transient iron fluorescence: new clues on the AGN disk/corona? Emanuele Nardini Horizon 2020 INAF/Arcetri AstroFIt2/MSCA in collaboration with: D. Porquet (CNRS/Strasbourg), J. Reeves (Keele+UMBC), V. Braito (INAF/Brera), A. Lobban (Keele), G. Matt (Roma Tre) The X-ray Universe 2017 - Roma, 6-9 June 2017
AGN X-ray spectral energy distribution Flux (kev 2 s 1 cm 2 kev 1 ) 0.3 1 3 soft excess warm/cold absorption X-ray continuum Compton hump Fe-K line(s) 1 10 100 Energy (kev)
Ark 120: the bare Seyfert prototype Nearest and brightest D = 144 Mpc FX = 7 x 10 11 erg/s/cm 2 M. Dovčiak Bare line of sight (Reeves+16b) NH < a few x 10 19 cm 2 BH mass known from reverberation mapping MBH = 1.5 x 10 8 MSUN All X-ray spectral traits of a radiatively efficient SMBH 2014 X-ray campaign (PI: D. Porquet) Four consecutive XMM-Newton orbits (7.5 days, net exposure 330 ks) Chandra HETG spectrum overlapping with XMM#2 + XMM#3 (120 ks) NuSTAR observation simultaneous with XMM#3 (65 ks)
XMM time-averaged spectrum Data/Continuum Wrong! 2 broad Gaussians FWHM = 2x Hβ X-ray BLR closer to the BH than the optical BLR (Costantini s talk) 5.5 7.5 Rest-frame energy (kev)
XMM time-averaged spectrum Data/Continuum Wrong! 2 broad 2 narrow Gaussians FWHM BLR-like = 2x FWHM Hβ X-ray BLR disk closer line to the BH than the rin optical = 60 rg BLR (Costantini s q = 3, i talk) = 30º 5.5 7.5 Rest-frame energy (kev)
XMM time-averaged spectrum Data/Continuum Wrong! 2 broad 2 narrow Chandra Gaussians ΗΕΤG FWHM BLR-like Fe-K = 2x wings FWHM Hβ X-ray BLR noise disk closer line and/or to the BH than the rin variability? optical = 60 rg BLR (Costantini s q = 3, i talk) = 30º 5.5 7.5 Rest-frame energy (kev)
Fe-K variability, short timescales 0 50 100 Elapsed time (ks) 200 250 350 400 450 550 600 Observed energy (kev) 5.5 6.0 6.5 7.0 0.0 5.0 10.0 Excess emission (10 6 counts s 1 cm 2 ) Excess map technique, used to reveal energy/intensity modulation of Fe-K lines within long exposure observations, but at smaller BH mass (Iwasawa+04, Turner+06) Energy vs. time resolution: 100 ev x 5 ks (orbital time at Kerr ISCO) Image smoothing: elliptical Gaussian kernel with 250 ev x 15 ks FWHM
Fe-K variability, short timescales 0 50 100 Elapsed time (ks) 200 250 350 400 450 550 600 Observed energy (kev) 5.5 6.0 6.5 7.0 1.4 quiescent 0.0 5.0 10.0 Excess emission (10 6 counts s 1 cm 2 )
Fe-K variability, short timescales 0 50 100 Elapsed time (ks) 200 250 350 400 450 550 600 Observed energy (kev) 5.5 6.0 6.5 7.0 1.4 quiescent red flare 0.0 5.0 10.0 1.4 Excess emission (10 6 counts s 1 cm 2 )
Fe-K variability, short timescales 0 50 100 Elapsed time (ks) 200 250 350 400 450 550 600 Observed energy (kev) 5.5 6.0 6.5 7.0 1.4 quiescent red flare blue flare 0.0 5.0 10.0 1.4 Excess emission (10 6 counts s 1 cm 2 ) 1.4
XMM time-resolved spectra 1.4 quiescence red flare blue flare Data/Continuum 2σ 3.5σ Rest-frame energy (kev)
The orbiting hotspots scenario Transient red/blue structures with no obvious periodicity nor correlation with each other: short-lived, individual hotspots at several tens of gravitational radii? 0.5 Flux (10 2 kev 2 s 1 cm 2 kev 1 ) 0.5 r =30 40r g =217 228deg Flux 0 Rest-frame energy r =15 25r g =40 65deg 0 Rest-frame energy (kev)
The orbiting hotspots scenario Transient red/blue structures with no obvious periodicity nor correlation with each other: short-lived, individual hotspots at several tens of gravitational radii? Flux (10 2 kev 2 s 1 cm 2 kev 1 ) Data/Continuum 2.0 1.5 0.5 r =30 40r g =217 228deg Flux 0.5 0 as would be seen by Athena Rest-frame energy r =15 25r g =40 65deg 0 Rest-frame energy (kev)
Implications on the AGN corona Alternative explanations are still viable, e.g. disk instability (photon bubbles on suborbital timescales) or hybrid corona (no Fe-K feature from around the ISCO) The broadband picture: (Porquet s talk) Broad FeK feature and mild Compton hump (consistent with each other) suggest reflection in the disk at several tens of gravitational radii, while the soft excess might have a different origin (Comptonization in a warm, optically thick medium)
Implications on the AGN corona Alternative explanations are still viable, e.g. disk instability (photon bubbles on suborbital timescales) or hybrid corona (no Fe-K feature from around the ISCO) The broadband picture: (Porquet s talk) Broad FeK feature and mild Compton hump (consistent with each other) suggest reflection in the disk at several tens of gravitational radii, while the soft excess might have a different origin (Comptonization in a warm, optically thick medium)
A radially extended corona?
A radially extended corona? 1keV 10 kev 1keV 10 kev 1keV 10 kev Porquet+ in prep. and next papers in the Ark 120 series
Summary Evidence for rapid (several tens of ks) variability of Fe-K fluorescence in the bare Seyfert Ark 120, compatible with flares/hotspots, inhomogeneity and/or instability Are these physical conditions and the underlying processes common among AGN? Should we expect any implications on broad Fe-K features and SMBH spin measurements? To reveal any fine structure in the Fe-K profile and perform a proper time-resolved spectral analysis, large effective area AND high energy resolution (read: Athena) are needed. Ark 120 is possibly the most promising source to study the properties of the accretion disk/x-ray corona system in a nearby AGN, and of its flaring, transient component(s). Nardini et al. 2016, ApJ 832, 45